The invention relates to devices for cutting tubes formed by wrapping continuous plies of paperboard or the like about a mandrel and adhering the plies together so as to form a continuous tube that is advanced along the mandrel to a cut-off apparatus where the tube is cut into sections of desired length. The invention relates more particularly to devices for cutting non-circular tubes formed in this manner.
Tubes formed from plies of fibrous material such as paperboard or the like are used for many purposes, including containers for consumer products. Many such containers are round in cross-section, for example, cans for refrigerated dough, juice cans, cans for snack foods, and many others. Round containers are typically produced by spirally winding paperboard plies and other plies such as liner plies and outer label plies onto a round mandrel to form a tube on the mandrel. The tube is engaged by a spiral winding belt that helically advances the tube along the mandrel to a cut-off apparatus where the tube is cut into predetermined lengths for later processing to form containers. The cut-off apparatus generally comprises an arrangement of saw blades that are pivoted into engagement with the tube at one side thereof. The saw blades are mounted on a moving carriage that moves along with the advancing tube in the longitudinal direction so that the only relative movement between the tube and the saws is a rotation of the tube about its axis. Thus, the full circumference of the tube can be cut by the saw blade from the outside of the tube.
Non-circular tubes are usually formed in a different manner from round tubes. Rather than spirally winding the plies onto the mandrel, the plies are drawn linearly along and wrapped longitudinally about the mandrel. Thus, the tube does not rotate as it advances along the mandrel. Accordingly, it is not possible to cut the tube by a saw that engages only one side of the tube as is done with round tubes. Instead, the tube is conventionally cut by a plurality of knives that encircle the tube from the outside and are moved radially inwardly to cut the tube against the mandrel.
One drawback to the conventional cutting device for non-circular tubes is that it can be difficult to cut all the way through the thickness of the tube, particularly when the tube includes a non-paper liner as its innermost ply. Such liners typically include a polymer layer to serve as a moisture barrier, and frequently also include a metal foil layer to lend strength to the polymer layer and to act as a gas barrier. There can be problems in achieving a clean cut all the way through the liner ply in the conventional cutting process, because the liner can stretch and deform under the force of the knives.
The above needs are met and other advantages are achieved by the present invention, which provides a cut-off apparatus for non-circular tubes in which the tube is cut from the inside toward the outside so that the liner is the first ply to be cut by the knives. The liner can be cut cleanly because it is backed up by the paper plies of the tube body.
In accordance with one preferred embodiment of the invention, a cut-off apparatus for cutting a continuously formed tube being advanced along a longitudinal axis of the tube comprises a carriage movably mounted for translation along the longitudinal axis in forward and rearward directions respectively with and against the direction of movement of the advancing tube. The apparatus also includes a carriage drive system operable to drive the carriage in the forward and rearward directions such that the carriage is driven in the forward direction in synchronism with the advancing tube. Thus, the tube is generally stationary relative to the carriage during at least part of the forward movement of the carriage. The cut-off apparatus further includes a tube cutting system coupled to the carriage for reciprocating movement therewith. The tube cutting system comprises a tubular mandrel positioned to receive the advancing tube thereover, and at least one cutter assembly. The cutter assembly includes a plurality of radially movable knives mounted within the mandrel and an actuator for urging the knives radially outward. The mandrel defines an opening for radially outward passage of each knife therethrough so as to cut through a wall of the tube from an inside surface to an outside surface thereof.
Preferably, the apparatus includes at least one clamp assembly coupled to the carriage in a position radially outward of the tube on the mandrel, the clamp assembly including clamp members that are movable radially inwardly to engage the tube opposite the knives so as to restrain the tube against radially outward movement during cutting.
In order to cut more than one section from the tube at one time, the cut-off apparatus preferably comprises a plurality of the cutter assemblies spaced apart a predetermined distance along the longitudinal axis, and a like number of clamp assemblies spaced apart and aligned with the cutter assemblies. The clamp members of each clamp assembly preferably have tube-engaging surfaces configured to collectively engage substantially the entire outer perimeter of the tube. The tube-engaging surfaces preferably define recesses therein aligned with the knives such that the knives can extend at least partially into the recesses.
In one preferred embodiment of the invention, the knives are actuated by a cam that is axially movable by the actuator so as to cause a surface of the cam to engage radially inner ends of the knives and thereby urge the knives radially outwardly for cutting the tube. The cam preferably is attached to a control rod that extends out one end of the mandrel, the actuator being coupled with the control rod and operable to move the control rod to cause the knives to be urged radially outwardly. After a cutting operation, the knives are urged back to their radially inward starting positions by springs connected to the knives.
In a preferred embodiment of the invention, the drive system for the carriage includes a sensor operable to detect advancement of the tube in the longitudinal direction, a controller connected to the actuator and to the sensor and operable to determine a distance and speed of advancement of the tube based on a signal from the sensor, and a motor connected to the controller and coupled with the carriage for moving the carriage in the longitudinal direction. When the tube has been advanced a predetermined distance, the controller causes the motor to advance the carriage at the same speed as the tube and causes the actuator to actuate the cutter assembly to cut the tube into sections. The sensor preferably comprises a roller in rolling engagement with the tube and an encoder coupled with the roller. Based on the signal from the encoder, the controller can determine the distance the tube has traveled from the number of revolutions of the roller and a known diameter of the roller, and can determine the speed of the tube from the rotational rate of the roller. Once the tube has been cut into sections, the carriage is returned to its starting position to begin the process again.